Strategic and tactical missile detection and target detection require basically two functions. First, is the detection of the missile launch and the burning of the propellant during acceleration into the ballistic trajectory. Secondly, the missile must be tracked to determine where it is targeted. In the event of multiple launches, the number of missiles need to be counted and tracked at substantially the same time.
Traditionally, strategic and tactical missile launch detection and tracking systems use infrared surveillance techniques employed by satellite sensors. The satellite sensors are required to view the whole earth at one time because the missiles could be launched from any location. It is necessary to determine where the missile is going and, from the trajectory, to find where the missile is likely to hit with a high probability of detection. For example, it is usually required to have a probability of detection of at least 99% and to avoid a false detection to a probability of less than once per month.
Based on these requirements, satellite sensing systems have been developed that contain many individual picture elements or pixels so that the systems can detect, count and track missiles anywhere on the earth. In order to track missiles to the accuracy required, it is generally necessary that the pixels have an extremely high resolution so that they can observe about a 1.5 kilometer square grid on the earth every few seconds. To do this with a staring array several millions of pixels are often needed. Surveillance systems using these large staring arrays are quite heavy (for example, about 6,000 to 8,000 pounds) due, in large part, to the multiplicity of pixel elements employed. To launch a satellite using such large staring arrays, expensive and heavy spacecraft launch vehicles, such as the Titan IV, must be used. This, of course, undesirably increases the cost of the project. The number of pixels can be reduced by scanning sensors but the pixels must be scanned at such a high rate that it produces an exceedingly large number of operations per second for the on-board satellite computer. Alternatively, all of the sensor data can be transmitted to the ground with a wide band data link. However, this is less desirable than on-board processing because it is less robust and radiation hard when compared with the narrow band data link that is used with on-board processing.
Many known missile detection systems sense infrared radiation in a single band. This band contains information about the missile as well as unwanted background. Another approach uses two discrete radiometers to cover two detection bands which are independently processed. Either approach suffers from problems when a strong background signal approximates or exceeds the missile within the detected band or bands. Hence, they are subject to a large number of false alarm indications when a detection threshold is set too close to the background clutter or to undesirably lower detection rates if the threshold is set too high.
It is an object of the present invention to overcome one or more of these problems.